Review on protection coordination strategies and development of an effective protection coordination system for DC microgrid

In this paper, common DC-fault detection methods have been reviewed. Effects of two line-to-line and line-to-ground fault types from various fault locations to operation of the DC system are presented. In addition, operation principle, strong and weak points of four main types of protection devices (including fuses, no-fuse circuit breakers, power-electronic protection devices and protective relays) are mentioned. Each different type of protection devices has the ability to protect and isolate different components of the DC microgrid (e.g. power converter, PV system, battery system, capacitor and others) under fault occurrences. The paper analyses possible protection coordination strategies of protection devices to ensure safety of any components in the DC microgrid. These summarized coordination strategies can be suitable for any DC microgrid configurations. In the next content, an effective protection coordination system of a real community-sized DC microgrid is developed, which use fast-acting fuses to replace no-fuse circuit breakers already installed at some certain locations in the DC microgrid. Aims of this improved protection coordination system are to shorten critical fault clearing time and get the cost effectiveness while still ensuring high selectivity, dependability and safety of the DC microgrid. As a result, the no-fuse circuit breakers placed at locations such as: output of PV arrays, output of the battery, output of the fuel-cell system, and terminals of power converters are efficiently replaced by the fast-acting fuses. Additionally, protection devices located at load feeders are suggested to use the relays to optimise the coordination time between main and back-up protection in case of faults occurring at the load feeders.